en Biology & physiology Biology & physiology پژوهشي Orginal research papers Sex steroids (testosterone, progesterone and 17&beta;-estradiol) play important roles in controlling reproduction and sexual maturity in teleosts. The aim of the present study was to evaluate the seasonal changes of these steroids in Rohu <em>Labeo rohita</em>. Forty gravid females and males <em>L. rohita</em> reared in different seasons (spring, summer, autumn, winter) were caught by a net with 1 cm mesh from earthen ponds of Aquaculture Research Institute, in south of Iran. The highest levels of 17&beta;-estradiol (122.8&plusmn;17.73 ng mL^-1), testosterone (0.11&plusmn;0.003 ng mL^-1) and progesterone (0.86&plusmn;0.01 ng mL^-1) in female fish were recorded in autumn. In addition, the highest concentration of testosterone in male was determined as 0.84&plusmn;0.003 ng mL^-1in autumn. The mean value of dissolved oxygen in four seasons (spring, summer, autumn, and winter) were 9.21&plusmn;0.77, 8.36&plusmn;0.51, 10.41&plusmn;0.9 and 13.14&plusmn;0.72 mg L^-1, with temperature 25.47&plusmn;1.07, 29.88&plusmn;1.42, 20.23&plusmn;0.69 and 14.63&plusmn;0.47 ◦C, respectively. Therefore, it can be inferred that progesterone was considered as the critical index for seasonal breeding selection. There was an appropriate condition in the mid winter for broodstock selection and breeding of fish with hormones manipulation. Sex steroids, Seasonal changes, Labeo rohita, Khuzestan, Iran 3063 3074 http://jifro.ir/browse.php?a_code=A-10-61-6&slc_lang=en&sid=1 H. Hosseinzadeh Sahafi h_hosseinzadeh@yahoo.com 100319475328460038361 100319475328460038361 Yes Iranian Fisheries Science Research Institute, Agriculture Research Education and Extension Organization (AREO), Tehran, Iran S. Dehghan Madiseh 100319475328460038362 100319475328460038362 No Iranian Fisheries Research Institute, South Aquaculture Research Center, Agriculture Research Education and Extension Organization (AREO), Ahvaz, Iran S. Koohilai 100319475328460038363 100319475328460038363 No Department of Marine Biology, Graduate School of Marine Science and Technology, Science and Research Branch, Islamic Azad University (IAU), Tehran, Iran M. Hamidinejad 100319475328460038364 100319475328460038364 No Department of Fishery, College of Agriculture And Natural Resource, Ahvaz Branch, Islamic Azad University, Ahvaz, Iran M. Velayatzadeh 100319475328460038365 100319475328460038365 No - Young Researchers and Elite Club, Ahvaz Branch, Islamic Azad University, Ahvaz, Iran